Blown plastic containers can be thermoformed using processes known in the art, including extrusion blow molding, injection blow molding, injection stretch and blow molding. The plastic container can be part of a finished package that includes a closure for the plastic container.
The above processes can be practiced in a technically sufficient and economic manner for containers that are formed from a single layer of material, as evidenced by their wide commercial application globally for packaging water, soda, beer, juice, and the like. Containers formed by the above processes can be formed from polyethylene, polypropylene, polycarbonate, and other materials. Such processes become more complicated if containers having multiple layers are desired.
Multi-layered containers can be desired for several reasons. For example, there may be a desire to include one or more barrier or coating layers to provide for chemical stability of the contents of the container. For example, if the content of the container is a laundry detergent or beverage, light may result in photo degradation of the content or components of the content that adversely impact performance or appearance of the laundry detergent or taste, appearance, and/or safety of the beverage. Sometimes, the substance contained in the container may react adversely with the material constituting the container. In this circumstance, a barrier layer between the substance contained in the container and the primary wall material can be beneficial. Sometimes, a barrier layer between the substance contained in the container and the primary wall material may be desired to reduce diffusion of the substance through the wall of the container.
In extrusion molding process, co-extrusion can be used to form a multi-layer extruded parison that is subsequently blown into a finished container. In injection molding process, the techniques of co-injection and over molding can be used to form multi-layer preforms that are subsequently blown into finished containers having multiple layers. In each of these processes, there can be multiple technical and challenges to providing containers having two or more layers. The technical challenges include providing for the desired thickness of each layer, obtaining adequate coherency of the multiple layers, and designing and operating the machinery capable of co-extrusion or over-molding. The present state of the art is capable of dealing adequately with these challenges at the expense of increased cost, increased complexity, reduction of speed of production of equipment, and more challenging quality control.
In view of these technical and economical limitations, there is a continuing unaddressed need for blown containers, including multi-layer containers that can be formed simply and inexpensively.